Carnitine is not an essential amino acid; it can be synthesized in the body. However, it is so important in providing energy to muscles (including the heart) that some researchers are now recommending carnitine supplements in the diet, particularly for people who do not consume much red meat (the main food source for carnitine). Carnitine has been described as a vitamin, an amino acid, or a metabimin (i.e. an essential metabolite). Like the B vitamins, carnitine contains nitrogen and is very soluble in water, and to some researchers carnitine is a vitamin (Liebovitz 1984). It was found that an animal (yellow mealworm) could not grow without carnitine in its diet. However, as it turned out, almost all other animals, including humans, do make their own carnitine; thus, it is no longer considered a vitamin. Nevertheless, in certain circumstances, such as deficiencies of methionine, lysine, or vitamin C or kidney dialysis, carnitine shortages develop. Under these conditions, carnitine must be absorbed from food, and for this reason, it is sometimes referred to as a "metabimin" or a conditionally essential metabolite. Like the other amino acids used or manufactured by the body, carnitine is an amine. But like choline, which is sometimes considered to be a B vitamin, carnitine is also an alcohol (specifically, a trimethylated carboxy-alcohol). Thus, carnitine is an unusual amino acid and has different functions than most other amino acids, which are usually employed by the body in the construction of protein. Carnitine is an essential factor in fatty acid metabolism in mammals. Its most important known metabolic function is to transport fat into the mitochondria of muscle cells, including those in the heart, for oxidation. This is how the heart gets most of its energy. In humans, about 25% of carnitine is synthesized in the liver, kidney, and brain from the amino acids lysine and methionine. Most of the carnitine in the body comes from dietary sources such as red meat and dairy products. Inborn errors of carnitine metabolism can lead to brain deterioration like that of Reye's syndrome, gradually worsening muscle weakness, Duchenne-like muscular dystrophy, and extreme muscle weakness with fat accumulation in muscles. Borum et al. (1979) describe carnitine as an essential nutrient for pre-term babies and individuals who are unable to eat a normal diet (e.g. non-ketotic hypoglycemics, kidney dialysis patients). In conditions such as kwashiorkor, cirrhosis, and heart muscle disease (cardiomyopathy) as well as in inborn errors of metabolism such as type IV hyperlipidemia and propionic or organic aciduria (acid urine resulting from genetic or other anomalies), carnitine is essential to life and carnitine supplements are valuable. Carnitine therapy may also be useful in a wide variety of clinical conditions. Carnitine supplementation has improved some patients who have angina secondary to coronary artery disease. It may also be worth a trial for patients with any form of hyperlipidemia or muscle weakness. Carnitine supplements may also be useful in many forms of toxic or metabolic liver disease and in cases of heart muscle disease. Hearts undergoing severe arrhythmia quickly deplete their stores of carnitine. Athletes, particularly in Europe, have used carnitine supplements for improved endurance. Carnitine may improve muscle building by improving fat utilization and may even be useful in treating obesity. Carnitine joins a long list of nutrients which may be of value in treating pregnant women, hypothyroid individuals, and male infertility due to the low motility of sperm. Carnitine deficiency is noted in abnormal liver function, renal dialysis patients, and severe to moderate muscular weakness with associated anorexia (http://www.dcnutrition.com). Carnitine is a biomarker for the consumption of meat.